PHOTOCHEMICAL HYDROGEN EVOLUTION FROM ALKALINE-SOLUTIONS OF XANTHENE DYES

The effect of the composition of five xanthene dyes (photoabsorber and photosensitizer) on the hydrogen photoproduction from aqueous solutions was investigated. It is suggested that triethanolamine (TEOA) can quench the excited singlet state of fluorescein in aqueous solution (1X10(-4) mol l(-1), pH 12.5). As a result, a reduced form of fluorescein is produced, which can further reduce H+ to H-2 in the presence of K2PtCl6 (5X10(-5) mol l(-1)). The quantum yield of H-2 photoproduction (Phi(H2)) is 0.024. For tetraiodofluorescein (erythrosin) in aqueous solution (1X10(-4) mol l(-1)), pH 12.5; K2PtCl6, 5X10(-5) mol l(-1)), Phi(H2) is as high as 0.30 owing to the inner molecular heavy atom effect. The quantum yields of fluorescence and intersystem crossing, Phi(F) and Phi(ISC), were measured and compared with Phi(H2) for all the investigated dyes. The results show an important ability of xanthene dyes to enhance hydrogen photoproduction from alkaline aqueous solutions.